It was narrated from Abu Hurairah that:
The Prophet said: "Sins are expiated by well-performed ablution despite difficulties, increasing the number of steps one takes towards the mosque, (and waiting for the next prayer after prayer)." (DE)
English reference (DE): Vol. 1, Book 1, Hadith 428 (DE)
Arabic reference (DE): Book 1, Hadith 463 (DE)